PixelCUBE Studios currently holds the #1 spot on iTunes’ list of free iPhone app downloads with their free app, The Impossible Test.

They noticed iPhone 4.1 and iPhone 4.0.1 in their usage stats and later tipped it to Engadget about it. The screenshot above shows that there are actually three versions of the iPhone 4.0 OS running on different devices i.e iPhone, iPod Touch and the iPad.

For now, we only know that the new iphone 4.0 OS is going to be soon unveiled on Thursday and iPhone 4.1 and iPhone 4.0.1 could be the future updates the new OS might receive.